'\" et
.TH PTHREAD_RWLOCK_TRYWRLOCK "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
pthread_rwlock_trywrlock,
pthread_rwlock_wrlock
\(em lock a read-write lock object for writing
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_rwlock_trywrlock(pthread_rwlock_t *\fIrwlock\fP);
int pthread_rwlock_wrlock(pthread_rwlock_t *\fIrwlock\fP);
.fi
.SH DESCRIPTION
The
\fIpthread_rwlock_trywrlock\fR()
function shall apply a write lock like the
\fIpthread_rwlock_wrlock\fR()
function, with the exception that the function shall fail if any thread
currently holds
.IR rwlock
(for reading or writing).
.P
The
\fIpthread_rwlock_wrlock\fR()
function shall apply a write lock to the read-write lock referenced by
.IR rwlock .
The calling thread shall acquire the write lock if no thread (reader
or writer) holds the read-write lock
.IR rwlock .
Otherwise, if another thread holds the read-write lock
.IR rwlock ,
the calling thread shall block until it can acquire the lock.
If a deadlock condition occurs or the calling thread already owns the
read-write lock for writing or reading, the call shall either deadlock
or return
.BR [EDEADLK] .
.P
Results are undefined if any of these functions are called with an
uninitialized read-write lock.
.P
If a signal is delivered to a thread waiting for a read-write lock for
writing, upon return from the signal handler the thread resumes waiting
for the read-write lock for writing as if it was not interrupted.
.SH "RETURN VALUE"
The
\fIpthread_rwlock_trywrlock\fR()
function shall return zero if the lock for writing on the read-write
lock object referenced by
.IR rwlock
is acquired. Otherwise, an error number shall be returned to indicate
the error.
.P
If successful, the
\fIpthread_rwlock_wrlock\fR()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_rwlock_trywrlock\fR()
function shall fail if:
.TP
.BR EBUSY
The read-write lock could not be acquired for writing because it was
already locked for reading or writing.
.P
The
\fIpthread_rwlock_wrlock\fR()
function may fail if:
.TP
.BR EDEADLK
A deadlock condition was detected or the current thread already owns
the read-write lock for writing or reading.
.P
These functions shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
Applications using these functions may be subject to priority inversion,
as discussed in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.291" ", " "Priority Inversion".
.SH RATIONALE
If an implementation detects that the value specified by the
.IR rwlock
argument to
\fIpthread_rwlock_trywrlock\fR()
or
\fIpthread_rwlock_wrlock\fR()
does not refer to an initialized read-write lock object, it is
recommended that the function should fail and report an
.BR [EINVAL] 
error.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.ad l
.IR "\fIpthread_rwlock_destroy\fR\^(\|)",
.IR "\fIpthread_rwlock_rdlock\fR\^(\|)",
.IR "\fIpthread_rwlock_timedrdlock\fR\^(\|)",
.IR "\fIpthread_rwlock_timedwrlock\fR\^(\|)",
.IR "\fIpthread_rwlock_unlock\fR\^(\|)"
.ad b
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.291" ", " "Priority Inversion",
.IR "Section 4.12" ", " "Memory Synchronization",
.IR "\fB<pthread.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
